apps.get_model() retrieves the model representation belonging to a particular historical migration state. That matters because importing the current model can expose fields and behavior that did not exist when the migration runs. section 10.2
Use it inside a RunPython function, whose required arguments are apps and schema_editor. Pass the application label and model name, then work with the returned model through its manager. section 10.2
Transforming Promoter data
Promoter = apps.get_model("promoters", "Promoter") retrieves the historical Promoter model. Iterating over Promoter.objects.all() can then populate full_name and common_name before saving each record. A reverse function retrieves the same historical model to restore the earlier fields.
